1. Field of the Invention
This invention relates to the development of light exposed film and is more particularly related to a system and method which utilize an electronically monitored and controlled film developer to develop heat processed photographic emulsions film.
2. The Present State of the Art
Processes for the development of photographic film use sheets or webs of material that require the transport of a developing activating agent from a storage reservoir or point of generation of the photographic film to the surface of the sheet or web. The developing or activating agent is generally consumed or destroyed in the process, necessitating the replenishing or regeneration of these agents along with the continued transport to the sheet or web surface. The transport is typically in the form of chemical compounds that must diffuse through a liquid or gaseous carrier to the web or sheet surface where they react and are consumed. Another type of transport is the transfer of heat from a source through a solid, liquid, gas, or combination of media, not only to the surface, but through the sheet or web material. Heat is lost in the process as it is transferred to the sheet or web.
Rate limitations, in either the generation of the activating agent or transport from the point of generation or storage reservoir to the web, result in non-uniform processing from the beginning of the sheet or web to the end of the sheet or web. In the case of photographic film, the non-uniformity in processing is observed as a decrease in development of the photographic film and a consequent drop in development density of the film from the beginning of the sheet or web to the end of the sheet or web. In the case of large web lengths, the difference in density of development of the film can be significant and result in poor overall quality of the development of the film.
In order to reduce the effects of rate limitations of developing or activating agents on the photographic film and to reduce the resultant film development quality problems, there are several approaches and practices currently used. One such practice is maintaining large storage reservoir volumes or capacities of activating agent to compensate for the activating agent which is consumed during processing of the photographic film. Examples of such use are large chemical bath volumes for chemically reactive systems for chemically developed film, and massive heat sinks for the processing of thermally developed photographic film. The large volumes or capacities approach of such systems is effective in reducing the effects of rate limitations of generation or replenishing of the activating agent. However, such large chemical reservoirs and heat sinks are costly both to operate and to store. Thus, it is desirable to find a system that would solve the present problem of quality of development density of the photographic film without incurring a large cost to do so.
Another problem with large storage reservoir volumes or capacities of activating agents is that this solution fails to address the limitations caused by transfer rate or transport in that there is no true regulation of the amount of activating agent being applied to the photographic film. Thus, a control problem exists in the development of the photographic film for both chemically activated systems and for thermally activated systems.
Another method used to reduce the effects of rate limitations and the resultant development density quality problems is incorporated into systems which add additional activating agent during the film development process. This approach could be the addition of chemical compounds or heat, depending on whether the system is a chemically developed photographic film system or a thermally developed photographic film system. With this type of compensating method, limitations on generation and replenishing of the activating agents are addressed, and by adding activating agent in excess of the actual usage rate, compensation can also be made for transport limitations. The transport rate from the storage reservoir to the sheet or web of photographic film is increased as a result of the larger activating agent driving force generated by the higher temperature or chemical concentration. The problem with this method is that it is difficult to control the activating agent being applied to the photographic film and thus requires adjustment of the temperature or chemical concentration of the activating agent after processing of each photographic film web or sheet in order to establish constant initial starting points and to maintain consistent results between processing successive batches of photographic film. Thus, it is desirable to develop a system which is able to control the amount and degree of activating agent that is applied to a photographic film, while minimizing shortages of such activating agent or excesses of such activating agent being applied to the photographic film during the film development process.
A particular problem exists with heat developed type photographic emulsions film in that this type of film is difficult to process and requires close temperature tolerances in its development. When the heat developed film reaches the development temperature, i.e., 240.degree.-300.degree. F., the emulsion side of the heat developed film becomes very soft and will stick to most surfaces in contact therewith. The soft emulsion side of the heat developed film makes it difficult to transport through a photographic film processor without some physical transport contact with the emulsion side of the heat developed film. Any such contact with the emulsion side of the heat developed film during the development process when the emulsion side is soft will leave a signature or imprint from such contact in the emulsion side of the heat developed film. Alternatively, such contact with the emulsion side of the heat processed film could transfer the emulsion to the object that came in contact with the emulsion side of the film.
Another problem with heat developed type film is that the sheet or web of the film tends to wrinkle or curl during film development.
A still further problem with heat developed type film involves processors for dry silver film. Processors for developing dry silver film may include electrostatic drums wherein the dry silver film is given an electrostatic charge, causing the dry silver film to cling to the electrostatic drum on a base side of the film which is opposite to the emulsion side of the film. With this system, the emulsion side of the film is not touched which gives the benefit of solving the aforementioned two problems related to contacting the emulsion side of the dry silver film. However, any small particles of dust on the electrostatic drums or on the base side of the dry silver film will isolate the dry silver film from the heat and thus cause an underdevelopment of the film in such areas of isolation.
A further problem with electrostatic drum processes is that the contact between the base side of the dry silver film and the electrostatic drums is not perfect and such imperfection causes pockets of air therebetween. The pockets of air further cause blotches of undeveloped dry silver film. When the dry silver film is stiff with a stable base side, the dry silver film will not cling to the electrostatic drums, and the larger sizes of dry silver film will tend to buckle and wrinkle so as to make the electrostatic drum method of processing the dry silver film undesirable for developing such stiff and stable base or larger sizes of dry silver film. Examples of such stiff, stable base dry silver film and larger size dry silver film are laser imaging films which are provided in large formats.
Flock roller processors also are used and work fairly well with paper products and certain types of thermally processed film that have a hard coating applied on top of the emulsion side of the film when the film is manufactured.
Flock roller processors, however, will not develop film that has a hard coating applied on top of the emulsion side of the film. The hard coating slows the exposure speed of the film, adds to the expense of making the film, and causes other exposure problems in modern laser imaging. Additionally, the flocked rollers shed fibers and particles and also have the detriment of becoming brittle and rough due to the presence of a stationary bar heater accompanying the flocked rollers which both heats and drags on the flock rollers.